1. Field of the Invention
The present invention relates to a hydraulic apparatus such as a swash-plate plunger type hydraulic pump or motor.
2. Description of the Related Arts
In such a swash-plate plunger type hydraulic apparatus, one end of each of a plurality of plungers is slidably fitted into a cylinder block in such an arrangement as to annularly surround a rotational shaft thereof and the other ends of the plungers are brought into sliding contact with a swash-plate for rotation along with the cylinder block, to thereby reciprocate the plungers. In this way, the ends of the plungers are moved along the swash-plate while being in sliding contact therewith, and hence there is often employed a structure where shoe members are swingably mounted on the ends of the plungers so that the shoe members can be in sliding contact with the swash-plate (for example, refer to Japanese Unexamined Patent Publication (Kokai) No. 57-70968). In this case, it is also well-known to use a retainer plate for pressing the shoe members against the swashplate since the shoe members are liable to be separated from the swash-plate when they are moved along the swash-plate at a high-speed in accordance with the rotation of the cylinder block.
FIG. 4 shows an example of such swash-plate plunger type hydraulic apparatus. The basic arrangement of both the conventional apparatus and the apparatus according to the present invention are shown in FIG. 4, which merely differ in the construction of the shoes 2, 20 and the retainer plate 3, 30. Reference numerals 2 and 3 denote the shoes and the retainer plate of the conventional apparatus, respectively, while reference numerals 20 and 30 designate the shoes and the retainer plate according to the present invention, respectively.
A spherical part 11 is provided at one end of each of plungers 10 which are slidably fitted into cylinder holes annularly arranged in the cylinder block 1 so as to surround a rotational axis C.sub.1, and each of the shoes 2 is swingably linked with the spherical part 11. These shoes 2 are in sliding contact with a slidably abutting surface 8a of the swash-plate member 8, and move along the surface 8a in accordance with the rotation of the cylinder block 1, to thereby reciprocate the plungers 10 within the cylinder holes 1a. During rotation, the retainer plate 3 presses the shoes 2 against the slidably abutting surface 8a so as to prevent the shoes from separating from the slidably abutting surface 8a. The retainer plate 3 is held in position through bearings 4 by means of a hold-down plate 5 secured to the swash-plate 8 with bolts.
As is apparent from FIG. 6 showing the prior art arrangement, this retainer plate 3 has a plurality of insertion holes provided corresponding to the shoes 2, and presses the slidable abutment 2b against the swash-plate 8 while inserting the necks 2a of the shoes 2 into the associated insertion holes 3a.
For this reason, the retainer plate 3 is caused to rotate along the inclined slidably abutting surface 8a of the swash-plate 8 together with the shoes 2. In this case, the plungers 10 to be linked with the shoes 2 rotate around the rotational shaft C.sub.1 cooperatively with the cylinder block 1 in a circulate orbit, whereby the shoes 2 each ovally move along the swash-plate. FIG. 5 shows the oval movement of each of the shoes 2. Since the retainer plate 3 is rotated along the swash-plate 8 while permitting the oval movement of each of the shoes 2, insertion holes 3a of the retainer plate 3 have the inner diameter D larger than the outer diameter d of the neck 2a of each of the shoes 2. FIG. 5 shows a positional relationship between the neck 2a and the associated insertion hole 3a every 90.degree. of rotation when the shoes rotate half along the swash-plate 8, and hence the inner diameter D of the insertion holes 3a is so made as to be larger than the outer diameter d of the neck 2a of each of the shoes 2 by a dimension to permit the oval movement of the shoes 2.
As a result, during the rotation of the cylinder block 1, the shoes 2 are allowed to slidably move along the swash-plate 8 while the outer periphery of the neck 2a of each of the shoes 2 comes in contact with the inner periphery of each of the insertion holes 3a of the retainer plate 3, which causes the shoes 2 to press against the retainer plate 3 for causing the rotation thereof.
On thus rotated retainer plate 3, there is exerted a reaction force (resistance) in the direction opposite to that of the rotation thereof, which acts on the shoes 2. Moreover, the position where the shoes are subjected to the reaction force varies depending on the movement of the shoes 2.
Furthermore, as shown in FIGS. 7 to 15, the shoe 2 that is subjected to the reaction force derived from the retainer plate 3 among the plurality of shoes 2 are intermittently changed according to the rotational angle of the cylinder block 1. FIGS. 7 to 15 show the relationship of the abutment between the neck 2a of each of shoes 2 and the associated insertion hole 3a of the retainer plate 3 for every 8.degree. of rotational angle when the cylinder block 1 having five plungers 10 is rotated. In FIGS. 7-15, the right-hand side corresponds to the side of the top dead center (T.D.C.) while the left-hand side corresponds to the side of the bottom dead center (B.D.C), and the relationship between the shoes 2 and the retainer plate 3 is shown in the case where the cylinder.block 1 is rotated by 8.degree. in the clockwise direction in each Figure from the state shown in FIG. 7 to the state shown in FIG. 15. Also, the reference point of the arrow A shown in the drawings designates the position where the neck 2a is in contact with the insertion hole 3a (the position subjected to the reaction force), and the direction of the arrow A signifies the direction of the reaction force. As clearly seen from these drawings, the shoe 2 to be subjected to the reaction force is intermittently changed in accordance with the rotation of the cylinder block.
FIG. 6 illustrates one of the shoes 2 which is subjected to the reaction force shown with the above-mentioned arrow A by way of example. As is clear from this figure, the reaction force acts on the imaginary center plane C.sub.2 in the axial direction of each of the insertion holes 3a of the retainer plate 3 (the imaginary center plane in the thickness direction of the retainer plate 3). In this case, the imaginary center plane C.sub.2 of the retainer plate 3 to be subjected to the reaction force A is spaced from the center O.sub.2 around which each of shoes 2 swings, and accordingly each of the shoes 2 is adversely subjected to a moment in the direction where it is caused to rotate or swing around the center O.sub.1 due to the reaction force A. For this reason, there arises a problem that the shoes 2 are tilted as shown by the dotted line in the FIG. 6, which causes the bottom surface 2c thereof to be separated from the slidably abutting surface 8a of the swash-plate 8, thereby obstructing the stable sliding movement of the shoes 2. In particular, the reaction force A is intermittently exerted on each of the shoes 2 as shown in FIGS. 7 to 15, which may bring about the inclination of the shoes 2.
Further, the conventional structure is such that a groove 2d serving as a hydrostatic bearing is provided at the bottom surface of each of the shoes 2, into which the oil pressure within the cylinder holes 1a is supplied through an oil passage (not shown) passing through each of the plungers 10 and a further oil passage 2e provided in each of the shoe 2. In such structure, there also arises a problem that the function of the hydrostatic bearing may be deteriorated due to the leakage of the oil out of the groove 2d if each of the shoes 2 is tilted as described above.
Moreover, the inclination of the shoes 2 may cause the neck 2a to roughly abut against the corners of each of the insertion holes 3a in the retainer plate 3, thus leading to the wear or scuffing of the associated part.